From: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "x86@kernel.org" <x86@kernel.org>,
Marcelo Tosatti <mtosatti@redhat.com>,
Gleb Natapov <gleb@redhat.com>,
"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v9 1/2] x86/kexec: VMCLEAR VMCSs loaded on all cpus if necessary
Date: Wed, 05 Dec 2012 15:55:37 +0800 [thread overview]
Message-ID: <50BEFDF9.9080601@cn.fujitsu.com> (raw)
In-Reply-To: <87zk1t4lt4.fsf@xmission.com>
于 2012年12月05日 04:14, Eric W. Biederman 写道:
> Zhang Yanfei <zhangyanfei@cn.fujitsu.com> writes:
>
>> This patch provides a way to VMCLEAR VMCSs related to guests
>> on all cpus before executing the VMXOFF when doing kdump. This
>> is used to ensure the VMCSs in the vmcore updated and
>> non-corrupted.
>
> Apologies for the delay I have been travelling, and I wanted
> to at least read through the code.
>
> Overall I think this is good but I have one nit, and I see one real
> problem with this code.
>
>> +/*
>> + * This is used to VMCLEAR all VMCSs loaded on the
>> + * processor. And when loading kvm_intel module, the
>> + * callback function pointer will be assigned.
>> + */
>> +void (*crash_vmclear_loaded_vmcss)(void) = NULL;
>> +EXPORT_SYMBOL_GPL(crash_vmclear_loaded_vmcss);
>> +
>> +static inline void cpu_emergency_vmclear_loaded_vmcss(void)
>> +{
>> + if (crash_vmclear_loaded_vmcss)
>> + crash_vmclear_loaded_vmcss();
>> +}
>
> The nit is the use of emergency instead of crash in the name.
ok, emergency -> crash
>
> The problem is that this is potentially a NULL pointer dereference if
> kvm-intel is removed. The easist fix would be in your second patch to
> just make it impossible to unload the kvm-intel module. Otherwise
> there the deference of crash_vmclear_loaded_vmcss needs to be rcu
> protected, with a syncrhonize_rcu after the pointer is set to NULL in
> the unload path.
Ah, thanks for this comment.
I think I will use the rcu machanism to solve the problem.
>
> Otherwise I have no objections to this code.
Thanks for your review. I will update the patch and resend it.
Thanks
Zhang Yanfei
next prev parent reply other threads:[~2012-12-05 7:57 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-27 3:25 [PATCH v9 0/2] x86: vmclear vmcss on all cpus when doing kdump if necessary Zhang Yanfei
2012-11-27 3:26 ` [PATCH v9 1/2] x86/kexec: VMCLEAR VMCSs loaded on all cpus " Zhang Yanfei
2012-11-27 12:18 ` Gleb Natapov
2012-12-03 13:46 ` Gleb Natapov
2012-12-04 20:14 ` Eric W. Biederman
2012-12-05 7:55 ` Zhang Yanfei [this message]
2012-11-27 3:26 ` [PATCH v9 2/2] KVM-INTEL: provide the vmclear function and a bitmap to support VMCLEAR in kdump Zhang Yanfei
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